The Hot Shield Fire Resistant Respirator Housing Model HS-4 is designed specifically for the Sundstrom brand, model SR-90 or SR-100 Half Face Respirator. The HS-4 provides a high degree of thermal protection to face & neck areas by way of design and proprietary materials, protecting both the user and the respirator. Constructed of CarbonX materials, a proprietary material tested to withstand over 2000 degrees Fahrenheit. The combination of the HS-4 and the Sundstrom SR-100 make for an efficient and user friendly protective device which users find comfortable wearing for extended periods. Allows fit testing of individuals as the respirator itself seals to the users face without fabric interference. Interior liners bsorb perspiration, adding to overall user comfort. Features 3M Scotchlite Reflective Trim for nighttime visibility . Fastens behind the neck (Velcro). One size fits all, machine washable.